4 Closers, Which one should I trade?

Percival. No question. He could go down for the season at any moment. Plus, he has value given his solid season this far.

Which one is getting you the best offers. None are elite but all of them are solid (and you already know their faults) so I would be moving the guy who can bring back the best outfielder in return. Valverde and Ryan are the guys personally I would want to hang on to but you have enough depth and probably have scored well enough in the save category to be able to afford to ship out any of these guys. Without seeing your roster it is hard to give suggestions but I wouldnt deem any of these guys untouchable and might try to move either Ryan or Valverde for a guy like a Cory Hart, Hunter Pence...players that are heating up, or similar type outfielders straight up (guys they might have drafted in 5th through 8th rounds that post solid numbers). You get very good production and the other guy doesnt feel like he is giving up his best outfielder and you dont have to make any crazy 2 for 1 deals or something else that weakens 2 positions to improve 1.

Trade Valverde or Gregg. Just don't get rid of Percival or Ryan.

Kevin Gregg. He is a real sketchy guy and the Marlins will slowly fall out of the race for the NL East and Wild Card.

Troy Percival (TB ] Like you said injured prone,old he can be a fluke in the first half , but it all depend who you get.

trade valverde or gregg or both for a solid fielding and hitting outfielder